1. Field of the Invention
The present invention relates to a blower fan.
2. Description of the Related Art
Japanese Patent Application Publication No. S60-145497 (JP60-145497A) discloses a conventional centrifugal blower for use in an air conditioner. As stated from line 11 of the upper right column to line 9 of the lower left column on page 2 and as shown in FIGS. 2 and 3 of JP60-145497A, the centrifugal blower includes a casing having a spiral surface 3. The radial length of the spiral surface 3 is increased from a spiral start point 7 radially closest to an impeller 1 along a rotation direction M of the impeller 1 in proportion to the rotation angle. An axial length F is constant in a section B extending from the spiral start point 7 to a first midpoint 8. A first slant surface 10 is formed in a section C extending from the first midpoint 8 to a second midpoint 9. In the section C, the axial length F is increased in proportion to the rotation angle. The axial length F is constant in a section D extending from the second midpoint 9 to a spiral end point 11. An inclination angle of a second slant surface 12 is increased to secure an equal cross-sectional area as the axial length is increased in proportion to the rotation angle. An inclination angle of a third slant surface 14 is changed to increase in a section E extending from the spiral end point 11 to a discharge midpoint 13. A flow path of a rectangular shape is enlarged at an appropriate enlargement angle in a section G leading to an outlet port 6. In lines 11 and 12 of the right lower column on page 2, JP60-145497A discloses that this configuration provides an increased flow path area and realizes enhanced blowing performance and reduced noise.
Japanese Patent Application Publication No. 2003-69265 (JP2003-69265A) is directed to a conventional small-size cooling fan for cooling an MPU of a notebook PC or the like. As recited in paragraph [0015] and as illustrated in FIGS. 1 and 3 of JP2003-69265A, the small-size cooling fan includes a rotating fan body 8 and a motor which are arranged within a flat fan housing 7. An air discharge port 9 is provided at one side of the fan housing 7. A backflow-preventing wind tunnel portion 10 leading to the air discharge port 9 is formed outwards of the tip ends of blades of the rotating fan body 8 in the fan housing 7. In paragraph [0018], JP2003-69265A discloses that, since an inner height of the wind tunnel portion 10 is set greater than an inner height of a fan chamber, a wind path of the fan is secured by the backflow-preventing wind tunnel portion 10 while the backflow of wind from the air discharge port 9 to the fan portion is prevented by the backflow-preventing wind tunnel portion 10 having a sharply increased space.
As one example of a conventional small-size cooling fan for use in a notebook PC, there is available a cooling fan in which an air intake port is provided around a motor fixing portion of a thin housing and an air discharge port is provided on a side surface of the housing. In this cooling fan, there are provided ribs for connecting the motor fixing portion to the portion around the air intake port.
In a notebook PC, the gap between an air intake port of a cooling fan and other members such as a PC housing, for example, is kept narrow. This makes it difficult to increase an air intake quantity and imposes a limitation in increasing an air blowing quantity. If the housing of the cooling fan is made thin to increase the gap, there is a possibility that the strength of ribs may be reduced and the requirements in a drop impact test cannot be complied with.